This invention relates to an underwater ultrasonic wave detection system for detecting the presence and location of objects such as schools of fish and the sea bottom around a ship, and more particularly to a drive mechanism for varying the orientation of a transducer in both azimuth and elevation while stabilizing the transducer against the pitching and the rolling of a ship.
This type of equipment employs an electro-acoustic transducer for transmitting the sound energy and for receiving echoes from objects in the field under investigation. Conventional equipment projects the transducer downward under the keel of a ship to a scanning position and rotates the transducer about a vertical axis and/or a horizontal axis, whereby the face of the transducer and the sound beam emanating therefrom are oriented in any specific vertical and/or horizontal directions under the ship, as disclosed in the specification and drawings of a U.S. Pat. No. 2,759,783. Since the transducer 20 therein is rotatably attached to a lower end of a lift shaft 186 and is fixedly connected to the ship, the sound beam moves with the movement of the ship when the ship either rolls and/or pitches, thereby tending to introduce errors in ranging and locating objects.
Accordingly, an object of this invention is to stabilize the transducer, so that it is not subject to angular motion because of the rolling and pitching of the ship on which the equipment is mounted.
Prior art equipment, however, for merely stabilizing the transducer against the pitch and roll motion of a ship have been disclosed in U.S. Pat. No. 2,832,944 and in Japanese Utility Model publication Zitsukosho No. 47-6381. This type of equipment, however, includes a motion sensing device, such as a gyroscope, which produces output signals corresponding respectively to the number of degrees of roll and to the number of degrees of pitch. These output signals are fed through respective conventional amplifiers to a scan drive motor and a tilt drive motor so as to correct for the pitch and roll motion of the ship, thereby always enabling the face of the transducer to be oriented in a desired direction. Consequently, the prior art equipment, becomes relatively bulky and costly, and the requirement of a high-degree of technical knowledge and information in the manufacture, installment, adjustment and maintanance of the sophisticated prior art equipment makes inappropriate their use in smaller ships such as fishing vessels.
Accordingly, another object of the invention is to provide a transducer mounting, driving and stabilizing device wherein the transducer is mechanically driven and which is compactly constructed and which can maintain the face of the transducer and the sound beam oriented in any specific direction in spite of the pitching and rolling of the ship, whereby the foregoing disadvantages and drawbacks can be eliminated.